diff --git a/src/websockets/sync/connection.py b/src/websockets/sync/connection.py
index 8b9e06257..12046d7ea 100644
--- a/src/websockets/sync/connection.py
+++ b/src/websockets/sync/connection.py
@@ -226,6 +226,9 @@ def __exit__(
         else:
             self.close(CloseCode.INTERNAL_ERROR)
 
+    def __del__(self) -> None:
+        self.close()
+
     def __iter__(self) -> Iterator[Data]:
         """
         Iterate on incoming messages.